Numerical analysis of the activated combustion high-velocity air-fuel (AC-HVAF) thermal spray process: A survey on the parameters of operation and nozzle geometry

WC-12Co coatings deposited by an activated combustion-high velocity air-fuel (AC-HVAF) spray process can improve surface quality and prolong the service life of parts. It is of considerable significance to quantitatively reveal the impact of process parameters on spraying behavior to improve high-quality coatings. In this study, a combustion model and a discrete phase model (DPM) are established based on the computational fluid dynamics (CFD) method. The flame flow characteristics (including pressure, temperature, velocity, and Mach number), mass fraction of the gas components, and particle flight characteristics (including temperature and velocity) are calculated. The results show that the Air/Fuel (A/F) ratio directly determines the maximum temperature of thermal spraying. When the A/F ratio remains constant, the temperature and velocity of the particles increase as the mass flow of the reactants increases. However, a higher A/F ratio and flow rate of the reactant increase the risk of particle oxidation. It is further found that a reduction in the Laval nozzle throat diameter increases the particle velocity; however, these changes do not obviously affect the particle temperature. The reduced Laval nozzle divergent angle causes an increase in the particle temperature and velocity. The longer the length of the Laval nozzle divergent part, the higher the temperature of particles. When its length is 190 mm, the particle velocity reaches the highest value.